Furukawa, Toshiaki A.

Honda, Michitaka

Yamamoto, Kazumichi

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European Journal of Cardio-Thoracic Surgery 46 (2014) 150 LETTER TO THE EDITORdoi:10.1093/ejcts/ezt454 Advance Access publication 11 September 2013Video-assisted thoracoscopic surgery lobectomy or open lobectomyfor non-small-cell lung cancer? Minimizing selection biasin observational studiesKazumichi Yamamotoa,*, Michitaka Hondab and Toshiaki A. Furukawaca Service of Otorhinolaryngology, Head and Neck Surgery, Lausanne University Medical Center (CHUV), Lausanne, Switzerlandb Department of Gastroenterological Surgery, Cancer Institute Ariake Hospital of JFCR, Tokyo, Japanc Department of Clinical Epidemiology, Kyoto University Graduate School of Medicine/School of Public Health, Kyoto, Japan* Corresponding author. Service of Othorhinolaryngology, Head and Neck Surgery, Centre Hospitalier Universitaire Vaudois (CHUV),Rue du Bugnon 21, 1011 Lausanne, Switzerland. Tel: +41-21-3141111; e-mail granada@d3.dion.ne.jp (K. Yamamoto).Received 17 June 2013; accepted 13 August 2013Keywords: Non-small-cell lung cancer • Video-assisted thoracoscopic surgery lobectomy • Open lobectomy • Prospensity score matchingWe have read with interest the paper by Hanna et al. [1], compar-ing oncological outcomes between video-assisted thoracoscopicsurgery (VATS) lobectomy and open lobectomy for non-small-celllung cancer (NSCLC) using propensity score matching, to minimizeselection bias in the retrospective cohort in their hospital. To date,more and more surgeons have performed VATS lobectomy forearly NSCLC and concern for its long-term oncological outcomesis emerging. However, most of the reports on this issue are retro-spective and only one randomized trial has been reported so far,as the authors correctly note [2]. Non-randomized comparisonsbetween treatments are subject to selection bias, because we‘select’ the cases for VATS lobectomy or for other approaches. Twosystematic reviews and meta-analyses have been published [3, 4],but they are not exempt from the selection bias either, becausethey themselves are based on retrospective cohort studies.Hanna et al. tried to minimize this selection bias in the retro-spective cohort by using propensity score matching, and this willbe effective for this purpose when properly and ideally con-ducted. However, we ﬁnd several important questions in statisticalmethods of this study. Propensity score is developed to minimizelarge differences of the observed covariates in observationalstudies, which would lead to biased results. Propensity score itselfis deﬁned as ‘the conditional probability of being treated giventhe individual’s covariates’ [5]. And, therefore, propensity scorematching should be performed to match VATS lobectomy andopen lobectomy with regard to similar patient backgrounds basedon the preoperative information. The authors used ﬁve variablesto construct their propensity score, three of which, however,derive from postoperative pathological information. These cannotlogically inﬂuence the choice of a surgical procedure. And aftermatching the cases between VATS lobectomy and open lobec-tomy using propensity score based on these variables, they ana-lysed the prevalence of preoperative comorbidities, rates oflymph node samplings and long-term oncological outcomes. Wecannot help saying that such analysis is contradictory to the deﬁn-ition of propensity score matching, which predicts ‘the conditionalprobability of being treated given the individual’s covariates’. Onthe other hand, oncological outcomes between two groups mayhave no signiﬁcant difference, because they matched the casesbased on pathological T and N, which is deﬁned to predict onco-logical prognosis. If the authors wish to compare the differencebetween two groups based on postoperative pathological results,simple multivariate analysis should be chosen, even though theythemselves are not free from the selection bias in this retrospect-ive cohort.We believe that more preoperative information should beadopted for propensity score such as preoperative comobidity,clinical information of the tumour including clinical TNM stage,histology and location, as we routinely use to decide upon thetype of procedure preoperatively and, after matching the cases,oncological outcomes should be compared between two groupsaccording to pathological TNM stagings.REFERENCES[1] Hanna WC, de Valence M, Atenafu EG, Cypel M, Waddell TK, Yasufuku Ket al. Is video-assisted lobectomy for non-small-cell lung cancer oncologi-cally equivalent to open lobectomy? Eur J Cardiothorac Surg 2013;43:1121–5.[2] Sugi K, Kaneda Y, Esato K. Video-assisted thoracoscopic lobectomy achievesa satisfactory long-term prognosis in patients with clinical stage IA lungcancer. World J Surg 2000;24:27–30.[3] Yan TD, Black D, Bannon PG, McCaughan BC. Systematic review and meta-analysis of randomized and nonrandomized trials on safety and efﬁcacy ofvideo-assisted thoracic surgery lobectomy for early-stage non-small-celllung cancer. J Clin Oncol 2009;27:2553–62.[4] Whitson BA, Groth SS, Duval SJ, Swanson SJ, Maddaus MA. Surgery forearly-stage non-small cell lung cancer: a systematic review of thevideo-assisted thoracoscopic surgery versus thoracotomy approaches tolobectomy. Ann Thorac Surg 2008;86:2008–16.[5] D’Agostino RB Jr. Propensity score methods for bias reduction in the com-parison of a treatment to a non-randomized control group. Stat Med 1998;17:2265–81.Letters to the Editor / European Journal of Cardio-Thoracic Surgery150

Video-assisted thoracoscopic surgery lobectomy or open lobectomy for non-small-cell lung cancer? Minimizing selection bias in observational studies

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